In evaporative heat exchangers, heat is exchanged between a liquid, e.g., water, and the ambient air. The temperature of the liquid is reduced both by direct heat exchange with the air and by a partial vaporization of the liquid so that heat is removed in the form of latent heat of vaporization, the resultant vapor being removed in the exhaust stream leaving the tower.
In conventional cooling towers, the contact between the liquid and air is enhanced by means of a structure referred to as a packing or fill. The fill is commonly a lattice or framework over which the liquid trickles and/or films while at the same time being exposed to an ambient air stream. The heat exchange properties of a cooling tower are improved not only by increasing the liquid/air interface as the liquid proceeds through the cooling tower, but also by increasing the turbulence of the flow of both liquid and air.
The primary object of this invention is to provide a cooling tower wherein the interface of liquid and air is optimized to provide the maximum thermal heat exchange benefit per unit fan energy consumption per unit capital cost expenditure.
A still further object of this invention is to provide a cooling tower of high thermal efficiency and compactness wherein the admixing of liquid and air in a turbulent stream is improved in the smallest enclosure dimension.
A still further object of this invention is to provide a cooling tower wherein the air motive force equipment for providing an air stream through the tower is shielded and protected from corrosion by avoiding contact with the liquid, the entrained liquid droplets in the air stream or the humid plenum chamber both during normal operation, and during fan-off operation.
With these and other objects in mind, the cooling tower of the present invention comprises a housing having therein a fill spaced apart from fan wall of the housing. In the fan wall is a conventional means to propel an air stream over and through the fill. The face of the fill inclines such that the distance between the wall and the fill increases as the liquid travels downward over the fill. The fill, thus spaced apart from the fan wall mounting the air propulsion means defines a zone of turbulent airflow such that liquid droplet falling into the turbulent zone admix with the incoming air and are thereby driven against the fill facing whereat they are broken into mist, coalesce, fall farther down the fill and then again can drop into the turbulent zone. After passing downwardly over the fill elements and through the turbulent zone the liquid finally collects at the base of the tower in a sump where it can be recirculated or discharged as is required.
The term "forced draft cooling tower" is intended to refer to those cooling towers where the ambient air drawn into the interior of the tower by a propulsion means passes first through the propulsion means before having any contact with the fill within the interior of the tower housing. It also means that the plenum chamber during operation will be at a positive pressure with respect to atmosphere.
The term "induced draft cooling towers" is intended to refer to those cooling towers where the ambient air drawn into the interior of the tower housing passes through the fill and becomes laden with vaporized liquid prior to passing through the propulsion means. It also means that the plenum chamber will be at a negative pressure with respect to atmosphere.
The prior art devices can be distinguished from the present invention on a plurality of counts including the turbulent path of the air taken through the tower the placement of the propulsion means relative to the fill and the absence of any turbulent air zone where liquid drops flow other than into the fill. To the contrary, the prior art uniformly teaches that one should prevent, by means of louvers or vertical fill orientation, the liquid from entering any turbulent plenum zone.
For example, U.S. Pat. No. 2,872,168 shows a forced draft cooling tower such that the air propulsion means is mounted horizontally below liquid retaining louvered walls in the tower base. The plenum space is thereby a dry air zone with exhaust air exiting at the top of the unit.
U.S. Pat. No. 2,732,190 shows a double pumping unit having a vertical fill such that downwardly traveling liquid is not induced to leave the fill structure and move to a turbulent air zone. Further, the air exits upwardly.
Similarly, U.S. Pat. No. 3,286,999 also shows a tower with vertical fill wherein liquid is prevented from entering any turbulent air zone.
In other known commercial units, the drive mechanism is inside the tower housing so that it is subject to corrosion, and although the fill may be inclined for various reasons, the fill face is nevertheless louvered to prevent liquid from falling into a turbulent air zone defined between the fill wall and the fan.